Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

The annotations already declare destructiveHint=true and readOnlyHint=false, so the description doesn't need to re-state that it mutates the project. The description adds a key detail: it performs the fade in one call, implying it replaces manual multi-step keyframing. However, it doesn't explain what happens to existing keyframes or opacity settings, which is a gap. Since annotations cover the safety profile, a 3 is appropriate.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is a single, concise sentence that communicates the action and scope efficiently. It is front-loaded with the main purpose, uses no filler words, and is easy to parse. This is an excellent example of minimal, high-value prose.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

The tool has 6 required parameters and an output schema, so the description doesn't need to explain return values. However, it doesn't clarify the exact behavior of the fade (e.g., interpolation type, whether existing keyframes are overridden). For a mutation tool with destructiveHint=true, this lack of behavioral detail slightly compromises completeness. The core purpose is clear, but additional context on effects would improve it.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 50%: two parameters (fromOpacity, toOpacity) have descriptions ('0..1.'), and projectId has a description. The tool description does not explain the meaning of fromFrame/toFrame or elementId further, but the schema likely has enough context via property names. The description adds no new parameter semantics beyond the schema, so a baseline of 3 is correct given the coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Does the description clearly state what the tool does and how it differs from similar tools?

The description states a clear verb ('Fade') and specific resource ('a layer's opacity') plus the scope ('between two frames in one call'). It clearly distinguishes from siblings like 'set_layer_visible' or 'add_keyframe' by focusing on a single operation. This is precise and unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Does the description explain when to use this tool, when not to, or what alternatives exist?

The description implies when to use this tool (when you need to fade opacity over frames), but it doesn't explicitly state when not to use it or mention alternatives like 'add_keyframe' for more complex animations. There is no discussion of prerequisites or edge cases, so the guidance is minimal but not misleading.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.